Internal combustion engines combust a fuel and air mixture within cylinders driving pistons to produce drive torque. More specifically, air is drawn into an intake manifold of the engine through a throttle. The air is distributed to cylinders of the engine and is mixed with fuel at a desired air-to-fuel (A/F) ratio. The A/F mixture is combusted within the cylinders to drive the pistons.
The amount of fuel to the individual cylinders is controlled using, for example, port fuel injection. In order to provide the desired A/F ratio, the corresponding air rate of each cylinder must be accurately estimated. In order to accurately estimate the cylinder air rate, the state of the engine inlet air dynamics is characterized as either transient or steady-state. A corresponding cylinder air rate estimation approach is implemented based on the engine inlet air dynamics characterization.
When in steady-state, the manifold absolute pressure (MAP) is substantially constant over a predetermined time period. In this case, precise cylinder inlet air rate estimation is provided using a conventional mass air flow (MAF) sensor that is located in the engine inlet air path. The absence of any significant manifold filling or depletion in steady-state enables a direct correspondence between MAF and cylinder inlet air rate.
When transient, there is no direct correspondence between MAF and cylinder inlet air rate. As a result, the MAF sensor may not accurately characterize cylinder inlet air rate. This is primarily due to the significant time constant associated with manifold filling or depletion and MAF sensor lag. Transient conditions can arise rapidly during engine operation. Such transient conditions can result from a substantial change in the throttle position (TPS) or by any other condition that perturbs MAP. Any significant perturbation in steady-state operating conditions rapidly injects error in the MAF estimate of cylinder inlet air rate. Accordingly, if a MAF sensor is to be used for cylinder air rate, there must be a reliable determination of whether the engine is operating in steady-state or is transient.
Conventional methods of characterizing the inlet air dynamics as either steady-state or transient include certain disadvantages. For example, one method uses a single engine parameter (e.g., MAP) to detect both entry into and exit from steady-state. However, when using a single parameter to characterize the inlet air dynamics state, signal noise may result in inaccurate state detection. Further, the detection of transitions, especially out of steady-state, may be delayed while waiting for detailed analyses, such as analyses designed to reduce sensitivity to noise. If detection of a transition is delayed, cylinder inlet air rate estimation accuracy may be degraded.